Light projection



D. F. COMSTOCK. LIGHT PROJECTION.

APPLICATIQN, FILED mm1. 191e.

1,377,184. Patented. May 1o, i921.

UNITED sTATEs" DANIEL F. COMSTOOK, OF BROOKLINE, MilLSSl-XCIl-ITJ'SE'ITS,-'ASSIGrNORt TO KALM'S, l

PAT

ENT OFFICE;

COMSTOCK & WESCOTT, INC., 0F BOSTON, MASSACHUSETTS, A CORPORATION OF' l MASSACHUSETTS.

, LIGHT PROJECTION.

'Application mea Eprii 21, .1916. serian 92,759.

Toall whom t may concern.'

Be it known that I, a citizen ofthe United States, and resident of Brookline, in the county of Norfolk and State of Massachusetts, have invented new and useful Improvements in Light Projections, ofwhich `the following is a vspecification.

This invention relates to light projecting apparatus which has been designedparticularly for use` as a headlight for vehicles, although itis adapted to be used'for many other purposes.

In its broader aspects the inventionl has to `do with an application and utilization of the principle of the critical angle of reflection in a transparent, totally reflecting surface, for'y distributing or projecting energy into' a pre'- determined zone, While eliminating radiation outside of that zone.

In the more' specific application of the iny vention to automobile headlights, which I will describe as one useful exemplification of the principle of the invention, t e apparatus is adapted for preventing dazzling rays of light yfrom lbeing projected above an Vapproximately horizontal plane at about the level of 'the lamp without thel sacrifice of. `illuminating power in a zone belowv theV horizontal plane.

Two main obj ing headlight projectors are, first, to prevent rays of any considerable brightness from being projected upwardly above the level of the lamp or lamps and, secondly, to properly distribute the light within the restricted zone, and in many instances to concentrate as much light as possible just below the hori` zontal sothat the illumination may be effective as far as headlight. The first' of these objects could obviously be accomplished by tilting ortipin yiiiedhanically feasible, but this expedient would result in a sacrifice of horizontal con# centration Vof light since the intensecentral rays would'then strike kthe lroad at a short distance from the' headlight and only the weak raysnear -the edge of the beam would be projected' horizontally- Prior devices have' `been devised to elimi-v nate vthe objectionable 'dazzling effect of headlights by optically bending the raysk downwardly, but this `expedient, like that of mechanically tilting they beam, results in DANIEL F. CoMs'rocir,

ects to be attained in designa part ofthe rays which, if reflected, would be projected ina certain zone..

possible in front ofy the of the headlight downwardly, if this were able results may be' accomplishedv bygdirectmanner and obstructingall rays above the PatentedMay'idiezi.

'weak horizontal illuminatonwhich isiiiefy fective atk any .considerable distance from vthe headlight. i i

horizontal plane ofthe lamp ymeans of av i screen placed a considerable distancein advance of the lamp, butthismethod'isfobvi-` 65.5. ously impracticable forthe reason that,

screenk cannot be` suitably supported la suilif"A cient distance in front of the'lamp.

. .By my invention are desired resulten-ej'.

attained in a practical and efficientmanner by directing Lthe beam issuingfrom a lamp against a` reflecting surface, as for 'example a glass-air surface, which is so constructed l andarranged relative to the lamp thatceii-I tain rays will be reiected'and: projected 4into ka predetermined limited zone, whileflight M which, if reflected, would beprojected'out;

'side of the predetermined zone, for .example, above a horizontal plane, passes through l the reflecting surfaceby virtue Vof, ythe fact that all such rays strike the4 vreflecting surface at an `angle of incidence lessI than the For convenience,"Ieniploy the term criti- Vao rcritical angle.l Otherobjects of my inven' 'I `tion will be Ahereinafter madeapparent.

cal-angle reflector to designate 'any' reflectning means so constructed and arranged vas to re r act and transmit, according to the principleof the critical angle of incidence, all or f I have illustrated one'embodiment of my i invention 1n `the accompanyingl drawings wherein, y

Figure 1 is a diagrammatic, sectional view illustrating one arrangement of lamp', parabolic reflector and critical-angle reflector; Fig. 2 'is a perspective' view of oneforin of critical-anglereflector; and..`

Fig. '3 is a diagram showingy the general character of the distribution of light Afrom a headlight ofthe 4type' illustrated'in F ig. 1,

both with and without the present invention applied thereto.

In the diagrammaticfview shown in Fig. 1,'

A is a source of light located approximately at'the focalfpoin't of the pa'raltiolhz reflector' B, and C is'va prism of glass of suitable properties which affords fai criticalfangle reflecting surface at its rearface.'

If the source of light were a. point source and the reflector B, precise-ly parabolic, all

r of the reflected rays would be projected parallel to the axis of the reflector, but such conditions are only roughly approximated in the ordinary commercial headlight. As

a result, theheadlight beam is substantially conical with the relatively great intensity of the central :zone rapidly diminishing outwardly assliownby the curve a, 5,0, d, c

in Fig. 3; Thus lthedenSe portionof the rays from Ithe lamp'A, such as X, are reflected bythe parabolic reflector'in a direc-f f tion Y, approximately parallel tothe axis of the reflector; a part ofthe rays, such asV,

" yare reflected rearwardly as shown at XV; and

wardly as indicated aft S.

some of the rays, such as R. are vreflected for@ The reflecting prism C is so constructed y light and parabolicreflector that: first, the

central rays'such'a-s Y will be reflected by the prism C in substantially a horizont-al direction secondly, the rays rvsuch. 4 Si, which strike the glass-air surface at an angle to the normal greater than thecritical angle of incidenca'are reflected in avdirectionbe low the 'horizontal depending on their re'- spectivel anglesfof incidence; and thirdly,

ysubstantially]all rays such as W, lwhich strikethe glass-airy surface at an angle yless thanf'the critical angle of incidence, and

which, `if reflected, would lbe projected lin aydirection above the horizontal, pass through the glass-"air surface, That is,tlie reflecting prism C'is so constructed and arranged that the angie 5f incidence of ali rays w which,

if reflected, would be projected-upwardly,

,is less than lthe critical angle and substanjtially allofsuch raysarenot reflected but are refracted. For this purpose 1v have i found'that'a prism of ordinary glass havinga refractive index of 1.5 and a critical f yangle lof 41.7? is suitable. i

` f vided with ridges or (steps D having faces The upper surface of the prism C is pro- E and F arrangedtol minimize the refraction k'of the rays when kentering the prism. The

angles between the faces E and F may, if

desired, be made such that the average `re lfraotionjofthe direct rays from the lamp and of ktherays reflected from the parabolic 1 incidence of `the direct light varies fromthe Vaxis outwardly, a'still further refinement minimum.

. i f ymaybe vmade by making the anglebetween each lpaiiiof faces different so that the objectionable refraction of each face will be a proximately perpendicular to the axis of and positionedrelative to the source ofy However, excellent results may be obtained byfmaking the faces E and F parallel, respectively, and the faces E ap-A the parabolic reflector, since most of the reflected rays are substantially parallel to lthis axis.

As above stated, most lof the rays of light issuing' from the parabolic reflector are sub` stantially parallel to the axis of t-he reflector and furthermore the most intense light yissuing directly from the lamp will be in this direct-ion.' I preferably so position the headlight and the critical-angle reflector `relative to each otherand vto the horizontal that the ray A -C in Fig. 3, which strikes the reflector at the critical angle, is reflected horizontally or slightly therebelow. Substantiallyfall the light which'` if reflected,

would be projected above the horizontal, is

transmitted through the reflector as shown by the curve (1,22', c. Thus, the more intense central light c, (l, in Fig. 3 will be reflected as at'M, in Fig. l, in or slightly below a horizontal direction and thus afford a con- A.thejgla-ss-air surface at an angle of incidence greater'than the critical, as at O, will be projected on the roadway nearer to the vehicle where less light is ordinarily needed, and substantially all of the light striking the glass-air surface at an angle of incidence less lthan the critical angle, as at N,

I (which 'is alsoa comparatively small amount of the Vtotal light) will be refracted. This refracted light is not wasted but is projected forwardly'in the direction Q and illuniinates the surface immediately in front of the projector. Owing to the well known fact that light suddenly ceases to be reflected at the critical angle, the horizontal plane of discontinuity is' rendered sharp and distinct.

lVhile I have herein shown and described one form of my invention for illustrative purposes, and have disclosed and discussed in detail the construction and arrangement incidental tov one specific' embodiment thereof, it is to be understood that the invention is limited neit lier to the details nor the precise relative arrangement of parts,'nor to its-specific application herein shown. but that extensive deviations from the illus'- centrated beam whichwill vbe projected far trated form'or embodiment of the invention ample. torestrict light from a search light or other source in any desired manner. Moreover, the intention is applicable to 'invisible rays such as X-rays, ultra-violet or actinic rays, infra-i'ed or heat rays, electroing rays which are not parallel with said rays, a transparentvreflector obliquely disposed in the path of the beam of light at suc-h an angle that the parallel rays make substantiall critical angles of incidence with the re ector so that a part of one class of rays is transmitted and a part of the` other class of raysv is reflected, theparallel rays being so separated from the non-parallel rays as to produce a beam sharply defined on at least one side.

2. Projection apparatus comprising means for producing a concentrated beam of light having substantially parallel rays, a trans.- parent reflector obliquely. disposed in the path of the beam of light at such an angle that the parallel rays are incident tothe reflector at substantially the critical angle so that all rays making greater angles of incidence with the reflector are reflected and all rays making lesser angles of incidence with the reflector are transmitted throu h the reflector, whereby a beam of lig t sharply defined on one side is reflected from the reflector.

3. Projection apparatus comprising a source of radiant energy and a critical-angle reflector arranged to reflect and project rays in a predetermined zone, and to transmit rays which, if reflected, would be projected outside of said predetermined zone.

4. Projection apparatus comprising a source of wave radiation and reflecting-refracting means having a critical angle of incidence, the saidmeans being so disposed in the path of said radiation that a portion of said energy is reflected and restricted to a zone bounded on one side by a plane making an angle with a normal to said means substantially equal to the critical angle.

5. Projection apparatus comprising means for producing a beam ofradiant energy, and a critical-angle reflector in the path of the beam from said source arranged to refleet part of said beam in a predetermined zone, and to transmit only that part of said beam which, if reflected, would fall outside of said zone.

6. Light projecting apparatus comprising means for producing a beam of light, means for reflecting a portion of said light, said reflecting means refracting and transmitting all rays incident thereto within the critical angle, whereby a sharply defined zone of reflected light is produced.

7. A headlight comprising means for producing a beam of light, and means for reflecting a portion ofsaid beam in a zone reflecting means permitting all light to ass therethrough which, if reflected, woul be projected above said plane.

8. A headlight comprising means for producing a beam of light downwardly, a prism in the path of said beam, means on the upper surface 'of said prism to minimize refraction, and a total reflecting surface on the lower sideA of said prism, whereby concentrated light is reflected in a zone below a substantially horizontal plane and whereby that portion of the beam which, if reflected, would be projected upwardly, is transmitted and refracted downwardly and forwardly.

9. The method of producing a beam of light sharply defined on one side comprising producing a beam of light having substantially parallel rays and having some rayswhich are not parallel withsaid rays, and projecting the beam to a transparent reflector so that the parallel rays are incident to the reflector at substantially the critical angle, whereby the rays incident to the reflector at less than the critical angle are.

r` below a substantially horizontal plane, said A light sharply defined on one side comprising t producing a beam of light having substantially parallelrays and having some rays which are not parallel with said rays, and

f projecting the beam to a reflector at such an angle that the parallel rays are incident thereto at the critical angle, whereby the non-parallel rays deviating in one direction j from the parallel rays are transmitted and the other rays are reflected in the form of a; beam sharply defined on one side.

Signed by me at Boston, Massachusetts, this 17th day of April, 1916.

DANIELE. coMsTooK. 

